Engineering topics

Green, R. N.

Publications and source records attributed to Green, R. N..

At least 19 records

NASA NTRS2002

Early Radiometric Validation Results of the Ceres Flight Model 1 and 2 Instruments Onboard NASA's Terra Spacecraft

The CERES Flight Model 1 and 2 instruments were launched aboard NASA's Earth Observing System (EOS) Terra Spacecraft on December 18, 1999 into a 705 Km sun-synchronous orbit with a 10:30 a.m. equatorial crossing time. These instruments supplement measurements made by the CERES Proto Flight Model (PFM) instrument launched aboard NASA's Tropical Rainfall Measuring Mission (TRMM) spacecraft on November 27, 1997 into a 350 Km, 38-degree mid-inclined orbit. An important aspect of the EOS program is the rapid archival and dissemination of datasets measured by EOS instruments to the scientific community. On September 22, 2000 the CERES Science Team voted to archive the Edition 1 CERES/Terra Level 1b and Level 2 and 3 ERBE-Like data products. These products consist of instantaneous filtered and unfiltered radiances through temporally and spatially averaged TOA fluxes. CERES filtered radiance measurements cover three spectral bands including shortwave (0.3 to 5 micron), total (0.3 to less than 100 microns) and an atmospheric window channel (8 to 12 microns). The current work summarizes both the philosophy and results of validation efforts undertaken to quantify the quality of the Terra data products as well as the level of agreement between the Terra and TRMM datasets.

Priestley, K. J.↗

NASA NTRS2001

Determination of Unfiltered Radiances from the Clouds and the Earth's Radiant Energy System (CERES) Instrument

A new method for determining unfiltered shortwave (SW), longwave (LW) and window (W) radiances from filtered radiances measured by the Clouds and the Earth's Radiant Energy System (CERES) satellite instrument is presented. The method uses theoretically derived regression coefficients between filtered and unfiltered radiances that are a function of viewing geometry, geotype and whether or not cloud is present. Relative errors in insta.ntaneous unfiltered radiances from this method are generally well below 1% for SW radiances (approx. 0.4% 1(sigma) or approx.l W/sq m equivalent flux), < 0.2% for LW radiances (approx. 0.1% 1(sigma) or approx.0.3 W/sq m equivalent flux) and < 0.2% (approx. 0.1% 1(sigma) for window channel radiances.

Loeb, N. G.↗

NASA NTRS1995

Clouds and the Earth's Radiant Energy System (CERES) algorithm theoretical basis document: Geolocation, calibration, and ERBE-like analyses (subsystems 1-3) - volume 2

The theoretical bases for the Release 1 algorithms that will be used to process satellite data for investigation of the Clouds and Earth's Radiant Energy System (CERES) are described. The architecture for software implementation of the methodologies is outlined. Volume 2 details the techniques used to geolocate and calibrate the CERES scanning radiometer measurements of shortwave and longwave radiance to invert the radiances to top-of-the-atmosphere (TOA) and surface fluxes following the Earth Radiation Budget Experiment (ERBE) approach, and to average the fluxes over various time and spatial scales to produce an ERBE-like product. Spacecraft ephemeris and sensor telemetry are used with calibration coefficients to produce a chronologically ordered data product called bidirectional scan (BDS) radiances. A spatially organized instrument Earth scan product is developed for the cloud-processing subsystem. The ERBE-like inversion subsystem converts BDS radiances to unfiltered instantaneous TOA and surface fluxes. The TOA fluxes are determined by using established ERBE techniques. Hourly TOA fluxes are computed from the instantaneous values by using ERBE methods. Hourly surface fluxes are estimated from TOA fluxes by using simple parameterizations based on recent research. The averaging process produces daily, monthly-hourly, and monthly means of TOA and surface fluxes at various scales. This product provides a continuation of the ERBE record.

Wielicki, B. A.↗

NASA NTRS1989

Angular radiation models for earth-atmosphere system. Volume 2: Longwave radiation

The longwave angular radiation models that are required for analysis of satellite measurements of Earth radiation, such as those from the Earth Radiation Budget Experiment (ERBE) are presented. The models contain limb-darkening characteristics and mean fluxes. Limb-darkening characteristics are the longwave anisotropic factor and the standard deviation of the longwave radiance. Derivation of these models from the Nimbus 7 ERB (Earth Radiation Budget) data set is described. Tabulated values and computer-generated plots are included for the limb-darkening and mean-flux models.

Suttles, J. T.↗

NASA NTRS1988

Angular radiation models for Earth-atmosphere system. Volume 1: Shortwave radiation

Presented are shortwave angular radiation models which are required for analysis of satellite measurements of Earth radiation, such as those fro the Earth Radiation Budget Experiment (ERBE). The models consist of both bidirectional and directional parameters. The bidirectional parameters are anisotropic function, standard deviation of mean radiance, and shortwave-longwave radiance correlation coefficient. The directional parameters are mean albedo as a function of Sun zenith angle and mean albedo normalized to overhead Sun. Derivation of these models from the Nimbus 7 ERB (Earth Radiation Budget) and Geostationary Operational Environmental Satellite (GOES) data sets is described. Tabulated values and computer-generated plots are included for the bidirectional and directional modes.

Suttles, J. T.↗

NASA NTRS1986

Inversion methods for satellite studies of the Earth Radiation Budget - Development of algorithms for the ERBE mission

The Earth Radiation Budget Experiment carries a three-channel scanning radiometer and a set of nadir-looking wide and medium field-of-view instruments for measuring the radiation emitted from earth and the solar radiation reflected from earth. This paper describes the algorithms which are used to compute the radiant exitances at a reference level ('top of the atmosphere') from these measurements. Methods used to analyze data from previous radiation budget experiments are reviewed, and the rationale for the present algorithms is developed. The scanner data are converted to radiances by use of spectral factors, which account for imperfect spectral response of the optics. These radiances are converted to radiant exitances at the reference level by use of directional models, which account for anisotropy of the radiation as it leaves the earth. The spectral factors and directional models are selected on the basis of the scene, which is identified on the basis of the location and the long-wave and shortwave radiances. These individual results are averaged over 2.5 x 2.5 deg regions. Data from the wide and medium field-of-view instruments are analyzed by use of the traditional shape factor method and also by use of a numerical filter, which permits resolution enhancement along the orbit track.

Smith, G. L.↗

NASA NTRS1986

ERBE data inversion

Instruments on board the (presently two) satellites of the Earth Radiation Budget Experiment (ERBE) are collecting data for determining monthly averaged radiation exitances at the top of the atmosphere (TOA). To achieve the accuracy desired of the mission, radiances at the satellite are first calculated, with allowance made of sensor optical properties and the directionality of the TOA radiation field. The subsatellite surface type is classified to adjust for albedo changes and correction values are added for the types of cloud cover detected.

Smith, G. L.↗

NASA NTRS1984

A robust pseudo-inverse spectral filter applied to the Earth Radiation Budget Experiment (ERBE) scanning channels

Computer simulations of a least squares estimator operating on the ERBE scanning channels are discussed. The estimator is designed to minimize the errors produced by nonideal spectral response to spectrally varying and uncertain radiant input. The three ERBE scanning channels cover a shortwave band a longwave band and a ""total'' band from which the pseudo inverse spectral filter estimates the radiance components in the shortwave band and a longwave band. The radiance estimator draws on instantaneous field of view (IFOV) scene type information supplied by another algorithm of the ERBE software, and on a priori probabilistic models of the responses of the scanning channels to the IFOV scene types for given Sun scene spacecraft geometry. It is found that the pseudoinverse spectral filter is stable, tolerant of errors in scene identification and in channel response modeling, and, in the absence of such errors, yields minimum variance and essentially unbiased radiance estimates.

Avis, L. M.↗

NASA NTRS1984

Method for estimating errors for radiation budget based on a scanning radiometer

The conduction of the Earth Radiation Budget Experiment (ERBE) will involve the utilization of three sets of instruments. Each set consists of a nonscanning package and a scanning radiometer. The instruments will fly on the NOAA F and G operational satellites and on a dedicated spacecraft, the Earth Radiation Budget Satellite (ERBS). The ERBS will be in a 57 deg inclination orbit and will precess around the earth to provide sampling of the diurnal cycle of regions between + or - 57 deg latitude. The primary function of the scanning radiometer is to provide measurements for the calculation of the earth-emitted and absorbed solar radiation at the top of the earth-atmosphere system, averaged over 250 x 250 km regions. The present paper is concerned with errors found in these regional averages. Attention is given to details regarding the problem, scene identification probabilities, scene identification error effects, total pixel error, and errors due to regional averaging.

Smith, G. L.↗

NASA NTRS1983

Accuracy and resolution of Earth Radiation Budget Estimates

A numerical filter inversion technique that reduces wide-angle satellite measurements to top-of-the-atmosphere radiant exitances has been proposed for the Earth Radiation Budget Experiment (ERBE). The matrix formulation of this technique is presented, and the design of the numerical filter is discussed. The filter is smoothed with a singular value decomposition. The inversion process is simulated by generating synthetic measurements from a 24 degree spherical harmonic radiation field derived from Nimbus 6 ERB data. The numerical filter is applied to these measurements after they are corrupted with instrument error. The results are curves of expected error versus resolution area.

Green, R. N.↗

NASA NTRS1983

Accuracy of earth albedo estimates from wide-angle radiation measurements

The instantaneous resolution and accuracy that can be expected from two inversion techniques to be used in the Earth Radiation Budget Experiment (ERBE) are examined. It is shown that measurement errors are magnified by the numerical filter and that this magnification is a function of the magnitude of the inversion factor. By using singular value decomposition, these magnitudes can be reduced to improve the estimates. A simulation of the estimation process using an albedo field derived from scanning radiometer data shows that retaining 6 of the 13 singular values gives the best results. If there are no bidirectional model errors the medium-field-of-view data give the best estimates. However, when bidirectional model errors are considered, the wide-field-of-view measurements give better estimates since they are less sensitive to these errors.

Green, R. N.↗

NASA NTRS1981

Comparison of data inversion techniques for remotely sensed wide-angle observations of Earth emitted radiation

The shape factor, parameter estimation, and deconvolution data analysis techniques were applied to the same set of Earth emitted radiation measurements to determine the effects of different techniques on the estimated radiation field. All three techniques are defined and their assumptions, advantages, and disadvantages are discussed. Their results are compared globally, zonally, regionally, and on a spatial spectrum basis. The standard deviations of the regional differences in the derived radiant exitance varied from 7.4 W-m/2 to 13.5 W-m/2.

Green, R. N.↗

NASA NTRS1981

The effect of data analysis techniques on the interpretation of wide-angle longwave radiation measurements

Three different data analysis techniques - shape factor, parameter estimation, and deconvolution - have been applied to the same set of satellite radiation measurements to determine their effect on the estimated radiation field. The measurements are from a wide-angle, horizon-to-horizon, nadir-pointing sensor. The shape factor technique reduces each measurement to a radiant exitance at the top of the atmosphere by simple division by a constant. The parameter estimation technique processes all measurements together as a batch and defines the radiant exitance as a least-squares fit to the data. The deconvolution technique takes advantage of the fact that spherical harmonics are the eigenfunctions of the measurement operator. All three techniques are derived, and their assumptions, advantages and disadvantages are discussed. Their results are compared globally, zonally, regionally and on a spatial spectrum basis. All three techniques give comparable results for global parameters; however, results on a regional scale were quite different. The standard deviations of the regional differences in radiant exitance varied from 7.4 to 13.5 W/sq m. Of the three techniques, the parameter estimation technique produced the best regional results and is the choice of the author.

Green, R. N.↗

NASA NTRS1981

Deconvolution of wide field-of-view radiometer measurements of earth-emitted radiation. I - Theory

The theory of deconvolution of wide field-of-view (WFOV) radiometer measurements of earth-emitted radiation provides a technique by which the resolution of such measurements can be enhanced to provide radiant exitance at the top of the atmosphere with a finer resolution than the field of view. An analytical solution for the earth-emitted radiant exitance in terms of WFOV radiometer measurements is derived for the nonaxisymmetric (or regional) case, in which the measurements and radiant exitance are considered to be functions of both latitude and longitude. This solution makes it possible to deconvolve a set of WFOV radiometer measurements of earth-emitted radiation and obtain information with a finer resolution than the instantaneous field of view of the instrument. It is shown that there are tradeoffs involved in the selection between WFOV and scanning radiometers.

Smith, G. L.↗

NASA NTRS1981

Deconvolution of wide field-of-view radiometer measurements of earth-emitted radiation. II - Analysis of first year of Nimbus 6 ERB data

The theory of deconvolution considered by Smith and Green (1981) is applied to Nimbus 6 data in order to interpret the data with the maximum obtainable resolution. Attention is given to the data sample, sun-contaminated measurements, the measurement model, the deconvolution, the degree variance, the spherical harmonic coefficients, the geographical distribution of longwave radiation, time histories of zonal coefficients, and the effect of a grid system. Degree variance plots for 12 months of longwave radiation data show that the limit for a spherical harmonic representation of the Nimbus 6 wide field-of-view longwave data is 12th degree. The degree variance plots also reveal that most of the power is in the lower degree terms. Contour maps of the radiation field show the geographical distribution of earth emitted radiant exitance for each month.

Bess, T. D.↗

NASA NTRS1981

Simulation of a numerical filter for enhancing earth radiation budget measurements

The Earth Radiation Budget Experiment has the objective to collect the radiation budget data which are needed to determine the radiation budget at the top of the atmosphere (TOA) on a regional scale. A second objective is to determine the accuracy of the results. Three satellites will carry wide and medium field of view radiometers which measure the longwave and shortwave components of radiation. Scanning radiometers will be included to detect small spatial features. A proposal has been made to employ for the nonscanning radiometers a one-dimensional numerical filter which reduces satellite measurements to TOA radiant excitances. The numerical filter was initially formulated by House (1980). It enhances the resolution of the radiation budget along the satellite groundtrack. The accuracy of the numerical filter estimate is studied by simulating the data gathering and measurement inversion process. The results of the study are discussed, taking into account two error sources.

Green, R. N.↗

NASA NTRS1980

Deconvolution and analysis of wide-angle longwave radiation data from Nimbus 6 Earth radiation budget experiment for the first year

One year of longwave radiation data from July 1975 through June 1976 from the Nimbus 6 satellite Earth radiation budget experiment is analyzed by representing the radiation field by a spherical harmonic expansion. The data are from the wide field of view instrument. Contour maps of the longwave radiation field and spherical harmonic coefficients to degree 12 and order 12 are presented for a 12 month data period.

Bess, T. D.↗

NASA NTRS1980

The effect of directional radiation models on the interpretation of earth radiation budget measurements

A parameter estimation technique is presented to estimate the radiative flux density distribution over the earth from a set of radiometer measurements at satellite altitude. The technique analyzes measurements from a wide field of view, horizon to horizon, nadir pointing sensor with a mathematical technique to derive the radiative flux density estimates at the top of the atmosphere for resolution elements smaller than the sensor field of view. A computer simulation of the data analysis technique is presented for both earth-emitted and reflected radiation. The errors resulting from the assumed directional radiation model, spatial model and random measurement error have little effect on the global mean radiation. Zonal estimates were found to be more sensitive to the spatial model than to the directional radiation model. Results from analyzing medium field of view measurements showed a much greater sensitivity to the directional radiation model even on a global scale.

Green, R. N.↗